1. Field of the Invention
The present invention pertains to a speaker assembly that can accurately reproduce sound, and particularly low frequency sound. More particularly, the present invention pertains to a low-frequency speaker assembly that provides balanced and full range low-frequency sound reproduction in environments where interaction with surrounding surface(s) can cause deterioration in perceived sound, while improving low-frequency sound containment characteristics in order to avoid or reduce sound transmitted to adjacent space(s).
2. Brief Description of the Prior Art
Quality and enjoyment of music and sound, as reproduced in a listening space, can be determined by several key factors including, but not necessarily limited to, the following: (1) means by which sound is generated—this affects sound quality because it influences strength and type of sound patterns generated in a listening space; (2) presence of time-delayed acoustic reflections from walls, floors, ceilings, and/or other surrounding objects—these cause unevenness of sound which reduces clarity and detracts from quality of a listening experience; and (3) transmission of low frequency (“bass” range) sounds produced in a source space and transmitted to other spaces (such as, for example, adjacent rooms or properties) by air-borne and structure-borne paths—this can create a disturbance that may be disruptive and/or unpleasant to others. Such unwanted propagation of low-frequency sounds can be especially problematic in multi-unit residential buildings or outdoor venues.
In many cases, sound volume (or loudness) within a listening environment must be limited by the user in order to reduce negative effects, particularly negative effects of low-frequency sound transmission. As a result, a listener (such as, for example, a concert patron or residential user) is often not able to enjoy a sound reproduction system's full capabilities because reproduction of sound—and particularly low-frequency sound—limited or otherwise curtailed in order to reduce disturbance to adjacent property or living spaces. Unfortunately, such volume reduction can also reduce emotional impact and/or visceral quality of reproduced sound.
The physics of sound wave transmission can present a significant challenge to faithful reproduction of music or other sound, particularly in enclosed spaces. Residential and commercial structures, for example, can exhibit wide varieties of acoustic characteristics; such characteristics can be either desirable or detrimental to sound reproduction quality.
It is generally known that certain steps can be taken to improve sound reproduction quality, particularly at frequencies above 200 Hz. Such steps can include, without limitation, some or all of the following, either individually or in combination: use of electronic “equalizers” (band-pass filters), adjusting the type and placement of room furnishings, adjusting the type and placement of room appointments and adjusting the placement of speakers within a room or other space. Mid-range and high-frequency sounds can often be blocked from transmission to adjacent spaces or reduced by employing a variety of different building construction methods, such as, for example, a staggered-stud wall design that primarily attenuates mid-frequency and high-frequency sounds. However, low-frequency sounds are frequently transmitted by structural elements. As a result, such low-frequency sounds are generally more difficult to contain and control than mid-range and high-frequency sounds.
In addition, low-frequency sounds that are produced in a typical room are generally not distributed uniformly throughout said room, primarily due to said room's shape and dimensions. Consequently, the sound level and quality of low-frequency bass sounds in a conventional room can vary widely depending on listener position and can result in tonal unevenness, thereby being heavily reinforced at some room locations while being suppressed at other room locations. A consequence of said tonal unevenness is an unnatural musical effect and, thus, a loss of emotional impact of reproduced sounds (including, without limitation, music and film soundtracks). As a result, perception of a lower fundamental tone, such as, for example, a human voice (approximately 120 Hz) down to the lowest tone of musical interest (approximately 16 Hz), and spatial distribution of sound energy in a room becomes increasingly determined by room dimensions, room geometry, construction methods, construction materiality and objects present within said room.
An interaction of a plurality of sound waves with structural surfaces produces spatial acoustic patterns, or “modes,” in a listening area wherein some sound frequencies are magnified, or intensified, and others are reduced. Modes are present in all types of rooms and other enclosures, and often produce sonic irregularities that detract from the quality of reproduced sound. Although electronic equalization and speaker placement can partially address said irregularities, additional problems remain.
At low frequencies, room modes generally dominate a sound field at a listener location. Most low-frequency sound heard or felt by a listener, therefore, is not sound produced solely by a speaker, but rather a composite of both direct and reflected (reverberant) sound waves. As a result of said reverberation, quality and musicality of a bass sound in a room or a space can vary widely over a listening area and across its frequency range at any given location. Bass sound may seem full and resonant at some points in a room, while at other points, the sound may seem thin or lacking in fullness or power.
An operating principle of conventional low-frequency speaker designs is based on a theory of an acoustic “monopole.” A monopole sound source can radiate its acoustic output (sound energy) uniformly in all directions and generally in a spherical pattern. A variety of monopole speakers take advantage of certain design options in order to optimize electroacoustic efficiency, frequency range, physical size, and cost. A majority of these design options are usually one of four types of configurations that are variously called “horn” (including, folded horn), “infinite baffle” (including, transmission line), “acoustic reflex” (vented or ported) and “acoustic suspension” (“air suspension”). In said configurations, acoustic behavior of a physical structural enclosure or cabinet is a critical functional component in attainment of a speaker's overall performance, and thus, must be factored into cost of the system.
Consequently, a conventional monopole design has a variety of disadvantages, such as: (1) a sound radiation pattern that can stimulate a room resonance or mode, creating a reverberation, or “hangover” (a form of distortion), of a musical signal as well as uneven sound pressure levels throughout said room; (2) an acoustic excitation and transmission of sound to a floor surface or a wall surface, thereby creating vibration and noise outside of a listening area and often at a considerable distance depending upon a type of building construction; and (3) production of high sound pressure levels in near proximity to the speaker system, thereby inducing strong vibrations that are transmitted to and through support structures and reducing the noise attenuation effectiveness of said structures. Vibration created by this mechanism is efficiently transmitted to another space and an adjacent room, ceiling, and floor surface, which is an undesirable effect.
As a result, there is a need for an electroacoustic solution with a relatively small size that can (1) reduce excitation of acoustic room modes at low frequencies; (2) reduce the low-frequency sound energy transmitted from a source room to an adjacent room and/or space; (3) reduce coupling of vibration from the speaker directly to a building structure; and (4) provide sufficient acoustic output to reproduce a wide dynamic range and wide frequency range of modern recordings and soundtracks.